Yvo de Boer, the United Nations’ top climate official, announced Thursday that he would step down from his post in July to work in the private sector on environmental sustainability.

De Boer has overseen international climate talks for nearly four years, laboring without success to produce a legally binding pact to reduce global greenhouse gas emissions.

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His departure comes amid uncertainty as to whether the 193 member nations of the U.N. Framework Convention on Climate Change can produce a final treaty in Mexico in December.

“Working with my colleagues . . . in support of the climate change negotiations has been a tremendous experience . . . but I believe the time is ripe for me to take on a new challenge,” de Boer said in a statement.